Internal extrusion device and method of internal forming

ABSTRACT

The formation of non-circular bores in metal parts achieved by drilling a circular bore and ramming a mandrel (or punch) of the desired cross sectional configuration through the circular bore to cause a displacement of metal, primarily radial in character to complete the bore. The invention is particularly useful in working on steel, and the mandrel for this purpose should be of very hard, preferably tungsten carbide steel, whereby a fine micro smooth finish in the bore is produced. The pieces are worked on cold and may be heat treated thereafter for hardening. A typical example of the finished bore is one of hexagon shape.

United States Patent 1 Willmon INTERNAL EXTRUSION DEVICE AND METHOD OF INTERNAL FORMING [76] Inventor: LD Willmon, 226 36-A Nadine Cir.,

Torrance, Calif. 90505 [22] Filed: Jan. 30, 1974 [21] Appl. No.: 437,799

[52] US. Cl. 72/343; 72/370; 72/479 [51] Int. Cl. B21k 21/16 [58] Field of Search 72/343, 358, 479, 370

1,062,091 7/1959 Germany ..72/358 United Kingdom 72/479 [451 May 20, 1975 Primary ExaminerLowell A. Larson Attorney, Agent, or FirmHuebner 8L Worrel ABSTRACT The formation of non-circular bores in metal parts achieved by drilling a circular bore and ramming a mandrel (or punch) of the desired cross sectional configuration through the circular bore to cause a displacement of metal, primarily radial in character to complete the bore. The invention is particularly useful in working on steel, and the mandrel for this purpose should be of very hard, preferably tungsten carbide steel, whereby a fine micro smooth finish in the bore is produced. The pieces are worked on cold and may be heat treated thereafter for hardening. A typical example of the finished bore is one of hexagon shape.

5 Claims, 5 Drawing Figures INTERNAL. EXTRUSION DEVICE AND METHOD OF INTERNAL FORMING BACKGROUND OF THE INVENTION The formation of non-circular, as for example hexagonal, cross sectional bores is common practice, but the tools and methods presently in use present certain limitations. One method is to drill a round hole approximately equal to the minimum diameter of the finished bore, then driving through the bore a broach which cuts the bore to the desired cross sectional shape. A serious problem, especially in working on a steel piece, arises because the broach gets dull quite easily and starts tearing in the bore with a resulting rough surface. Such a surface cannot be cleaned up, the part or parts are not acceptable and must be discarded, the broach is sharpened and the work resumed.

Another method heretofore employed is by the use of a swedging machine. Starting with a round hole having a diameter at least equal to the maximum diameter of the finished bore, an arbor or mandrel of the hexagon cross section is inserted, then a force is applied against the outside surface of the piece being worked on, usually with an intermittent vibrating or pounding action. This drives circular fractions of the round bore against the flat areas of the mandrel by which the bore is shaped to completion. A difficulty here is that if the arbor is not tapered, it is difficult to remove, and if it is tapered the resulting bore is also tapered, which is usually undesirable.

SUMMARY OF THE INVENTION A primary object of the present invention is to form a hexagon or other non-circular bore with a fine micro finish by use of a mandrel with a highly polished surface which is driven through a preformed circular bore under suitably guided conditions to extrude metal in the piece worked on as distinguished from the cutting action of a broaching tool. Such a mandrel, if made of extremely hard steel should be useable indefinitely, obviously needs no sharpening, and will repeatedly turn out work of a high character.

The final bore is straight, that is to say, of uniform dimension throughout. During the forming, metal displaced will flow radially and to some extent axially, thus the final piece will have a slightly increased external diameter and very slightly increased length. No additional finishing of the surface of the bore is necessary, as the mandrel performs a burnishing function during its movement through the piece.

In carrying out the practice, the piece worked on may be supported on a sleeve disposed within a hobbing pot (or die), and the shank of the mandrel may be guided by a centering sleeve also within the hobbing pot, and by means of a hydraulic press the mandrel is forced through the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical view partly in section of the mandrel and workpiece in its proper relationship with the hydraulic press and associated elements ready to commence the extruding operation.

FIG. 2 is an exploded view of several of the elements illustrated in FIG. 1.

FIG. 3 is a section taken on the line 3-3 of FIG. 1.

FIG. 4 is a similar view to FIG. 1 after the mandrel has passed through the workpiece.

FIG. 5 is a perspective view illustrating the workpiece as a finished product.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Referring to FIG. 1, a tool 10 which may be referred to as a punch, or as an extruding mandrel, preferably is formed of the hardest available steel, such as 999 or 905 Grade Tungsten Carbide Steel, produced by General Electric Company, or equivalent. It comprises a head 11 and a shank 12. The head embodies (for purpose of illustration, and not of limitation) a straight hexagonal forming section 13 from which projects a tapered entry section 14. The shank 12 extends in the opposite direction from the forming section 13 and is of lesser diameter than the minimum diameter of the forming section.

This mandrel may be made from a very hard steel rod of the kind indicated by first grinding the round shank, then placing that in a chuck and dividing head on a surface grinder, and grinding the hexagon surfaces to form the head. Diamond grinding wheels preferably are used for the head, after which a very fine micro (reflective) finish is obtained by hand lapping with a diamond lapping compound. The forming section 13 has flat plane 7 surfaces parallel to the axis of the mandrel, or a back taper of 1 each side, and from each of these surfaces a continuation extends angularly toward the forward end of the mandrel.

The workpiece 20 which may be of normal steel (prior to hardening) and is worked on cold, is illustrated as a collar initially provided with an internal circular bore 21. The diameter of this bore is approximately equal to the minimum diameter of the final hexagon bore to be formed.

A base in the form of separable blocks 22 and 23 is used as the mounting for hobbing pot 25 and which is formed with a bore or through cavity 26. Mounted within the bore 26 is a support sleeve 27, the lower end of which rests on the blocks 22 and 23. This support sleeve has an internal diameter 28 of sufficient size for the mandrel to drop through, and its external diameter is sufficiently less than the diameter of the die bore 26 to provide a comfortable sliding tolerance as indicated at 30. The workpiece 20 is disposed on the upper end 31 of the support sleeve and its external diameter relative to the diameter 26 as seen at 32 should provide a snug slip by hand pressure but not slip by its own weight.

The mandrel 10, as shown in FIG. 1, is disposed with its entering section 14 extending into the circular bore 21 of the workpiece and it is properly positioned by a centering guide in the form of a sleeve 35 loosely slidable in the bore 26 and slidably encircling the shank 12 of the mandrel. As the initial position shown in FIG. 1, the centering guide rests on shoulders 36 where the head of the mandrel joins the shank.

In position to operate on the mandrel is a hydraulic press 43 which includes a plunger 44 of a piston of conventional design, not illustrated. The plunger is vertically aligned with the mandrel.

In operation, the plunger 44 is advanced against the end 42 of the mandrel and the advance continues until the head of the mandrel has moved completely through the bore 21 of the workpiece. This results in the conversion of the circular bore, shown in dotted lines in FIG. 3, into the hexagonal cross sectional bore, shown in full lines in FIG. 5, and numbered 50.

During advancement of the mandrel, the entry section first forms notches defining the location of the angular intersections for the hexagonal surfaces. As the mandrel moves farther, these notches expand in radial depth and width, enlarging and shaping the bore. Metal of the workpiece flows radially and to some extent axially during movement of the mandrel. The final configuration of the bore has been substantially attained by the time the forming section 13 reaches the workpiece, but the following action of the forming section assures a final set of the metal in the workpiece, and contributes a burnishing action to the wall of the bore with a resulting smooth very fine micro finish requiring no cleaning or polishing.

The ridges 52 and 53 at the intersections of the flat surfaces of the entry section and forming section, respectively, and the ridges 54 at the intersection of the entry section with the forming section are somewhat blunt or rounded, so that the action on the workpiece is extrusion as distinguished from broaching or cutting.

Such operation having been completed, and the head of the mandrel being temporarily lodged within the bore or cavity 28, the blocks 23 are separated by any well-known practice sufficiently to permit the support sleeve, the mandrel, the workpiece and the centering guide to fall through for removal; and the hydraulic plunger is retracted. The workpiece may be heat treated as desired.

Other non-circular shapes may be obtained by following the same principles as described for the hexagon mandrel.

Although I have described my invention in what I have conceived to be the preferred embodiment, it is recognized that departures may be made therefrom within the scope of my invention.

What I claim is:

1. An extrusion mandrel assembly for converting in a single operation a bore of circular cross section of a workpiece into a bore of non-circular cross section uniform throughout its length comprising a mandrel element embodying a forming section of the cross sectional configuration and dimensions of the finished non-circular cross sectional bore, a tapered entry section extending from the forming section, and a shank extending from the forming section in the direction opposite the entry section, and of a diameter no greater than the minimum diameter of the forming section, a support sleeve for said workpiece underlying said workpiece and of an exterior cross sectional dimension generally complementary with the exterior cross sec tional dimension of said workpiece, guide means independent of and overlying said mandrel element centering the shank of the mandrel element within the circular cross sectional bore of said workpiece, said assem- 4 bly further including a cylindrical hobbing pot circumferentially confining the support sleeve, workpiece and guide means, separable blocks supporting the hobbing pot and support sleeve, and power means for advancing the mandrel element to extrude said non-circular cross sectional bore.

2. An extrusion mandrel assembly for converting in a single operation a bore of circular cross section of a workpiece into a bore of non-circular cross section uniform throughout its length comprising a mandrel element embodying a forming section of the cross sectional configuration and dimensions of the finished non-circular cross sectional bore, a tapered entry section extending from the forming section, and a shank extending from the forming section in the direction opposite the entry section, and of a diameter no greater than the minimum diameter of the forming section, said forming section of said mandrel element includes flat surfaces lying parallel to the axis of the mandrel element and possesses a smooth, highly polished finish whereby movement of the mandrel element in forming the bore bumishes the surface of the latter and wherein the flat surfaces of the forming section are intersected by blunted ridges, and said entry section embodies flat surfaces tapering axially from the flat surfaces of the forming section, the said tapering surfaces being intersected by blunted ridges, each tapering section and its adjoining flat surface of the forming section being intersected by a blunt ridge, and power means for advancing the mandrel element to extrude said noncircular cross sectional bore.

3. An extrusion mandrel as defined in claim 2 in which the forming section is hexagonal in cross section.

4. An extrusion mandrel element as defined in claim 2 composed of very hard steel, the forming section possessing a very fine micro finish which will impart a very fine micro finish on the surface of a bore formed in a steel workpiece of lower hardness.

5. A method of converting a bore of circular cross section in a hard metal workpiece into a bore of noncircular cross section having a maximum diameter greater than the diameter of the circular bore and uniform throughout its length comprising the steps of: positioning the workpiece on a support having an opening therethrough of greater diameter than the maximum diameter of the bore to be formed, surrounding said support and with workpiece with a hobbing pot, axially aligning a mandrel element of harder metal than the workpiece and which embodies a requisite cross section with the circular bore, positioning an independent guide means within said hobbing pot in axial alignment with said support and said workpiece centering said mandrel element, and advancing the mandrel through the circular bore to extrude the metal of the workpiece. 

1. An extrusion mandrel assembly for converting in a single operation a bore of circular cross section of a workpiece into a bore of non-circular cross section uniform throughout its length comprising a mandrel element embodying a forming section of the cross sectional configuration and dimensions of the finished noncircular cross sectional bore, a tapered entry section extending from the forming section, and a shank extending from the forming section in the direction opposite the entry section, and of a diameter no greater than the minimum diameter of the forming section, a support sleeve for said workpiece underlying said workpiece and of an exterior cross sectional dimension generally complementary with the exterior cross sectional dimension of said workpiece, guide means independent of and overlying said mandrel element centering the shank of the mandrel element within the circular cross sectional bore of said workpiece, said assembly further including a cylindrical hobbing pot circumferentially confining the support sleeve, workpiece and guide means, separable blocks supporting the hobbing pot and support sleeve, and power means for advancing the mandrel element to extrude said non-circular cross sectional bore.
 2. An extrusion mandrel assembly for converting in a single operation a bore of circular cross section of a workpiece into a bore of non-circular cross section uniform throughout its length comprising a mandrel element embodying a forming section of the cross sectional configuration and dimensions of the finished non-circular cross sectional bore, a tapered entry section extending from the forming section, and a shank extending from the forming section in the direction opposite the entry section, and of a diameter no greater than the minimum diameter of the forming section, said forming section of said mandrel element includes flat surfaces lying parallel to the axis of the mandrel element and possesses a smooth, highly polished finish whereby movement of the mandrel element in forming the bore burnishes the surface of the latter and wherein the flat surfaces of the forming section are intersected by blunted ridges, and said entry section embodies flat surfaces tapering axially from the flat surfaces of the forming section, the said tapering surfaces being intersected by blunted ridges, each tapering section and its adjoining flat surface of the forming section being intersected by a blunt ridge, and power means for advancing the mandrel element to extrude said non-circular cross sectional bore.
 3. An extrusion mandrel as defined in claim 2 in which the forming secTion is hexagonal in cross section.
 4. An extrusion mandrel element as defined in claim 2 composed of very hard steel, the forming section possessing a very fine micro finish which will impart a very fine micro finish on the surface of a bore formed in a steel workpiece of lower hardness.
 5. A method of converting a bore of circular cross section in a hard metal workpiece into a bore of non-circular cross section having a maximum diameter greater than the diameter of the circular bore and uniform throughout its length comprising the steps of: positioning the workpiece on a support having an opening therethrough of greater diameter than the maximum diameter of the bore to be formed, surrounding said support and with workpiece with a hobbing pot, axially aligning a mandrel element of harder metal than the workpiece and which embodies a requisite cross section with the circular bore, positioning an independent guide means within said hobbing pot in axial alignment with said support and said workpiece centering said mandrel element, and advancing the mandrel through the circular bore to extrude the metal of the workpiece. 